Molten salt batteries are produced using methods that are the same as those used for other non-aqueous electrolyte secondary batteries. Patent Document 1 discloses a method for producing a non-aqueous electrolyte secondary battery by using an organic electrolyte liquid as an electrolyte. In this production method, a battery container that houses a positive electrode and a negative electrode is first placed in a chamber. Next, the chamber is subjected to a vacuum and heating so as to dry the battery container and remove moisture. The chamber is then returned to normal pressure and an organic electrolyte liquid is injected into the battery container.
In this case, moisture is removed from the organic electrolyte liquid at the organic electrolyte liquid production stage. However, the organic solvent used in the organic electrolyte liquid has physical properties, such as boiling point, that are similar to those of water. Therefore, removing water from an organic electrolyte liquid requires a refining step, such as precision distillation, as disclosed in Patent Document 2 for example. Moreover, if moisture is present in a secondary battery, resistance increases and charging and discharging capacity decreases due to hydrolysis of the electrolyte. In addition, long term use of secondary batteries leads to concerns regarding battery deterioration. Therefore, moisture removal treatment is carried out in non-aqueous electrolyte secondary battery production processes.
However, when producing molten salt batteries also, it is possible to remove moisture when producing a molten salt that forms an electrolyte. However, molten salts are polar hygroscopic substances. Therefore, when storing or transporting molten salts following production or when producing batteries, there are concerns that molten salts will be affected by atmosphere and tools and absorb moisture. As a result, it is possible to use the production methods disclosed in the above-mentioned documents for molten salt batteries, but it is not possible to achieve reliability that is similar to, or greater than, that of conventional secondary batteries. That is, there are concerns that the performance of secondary batteries will deteriorate over long periods of time as a result of water being contained in molten salts.